First-Principles Insights into Excitonic and Electron-Phonon Effects in van der Waals Heterostructures

TL;DR

This study uses first-principles calculations to analyze the electronic and excitonic properties of a ZrS2/HfS2 van der Waals heterostructure, revealing temperature-dependent effects and potential for optoelectronic applications.

Contribution

It provides the first detailed theoretical investigation of the excitonic and electron-phonon effects in ZrS2/HfS2 heterostructures, including temperature-dependent optoelectronic properties.

Findings

The heterostructure has an indirect band gap of 2.60 eV and a Type-I alignment.

Exciton binding energy is 0.71 eV, reduced from monolayers.

Temperature causes a redshift in the optical gap, with a 0.04 eV zero-point renormalization.

Abstract

Motivated by the successful synthesis of isolated ZrS2 and HfS2 transition metal dichalcogenide (TMD) monolayers and inspired by their nearly identical lattice constants, we construct and investigate a vertical ZrS2/HfS2 van der Waals (vdW) heterostructure. Using first-principles calculations based on density functional theory (DFT) and many-body perturbation theory (MBPT), we explore its electronic, optical, and excitonic properties, with particular emphasis on excitonic effects and their temperature dependence. Based on the GW method, the ZrS2/HfS2 vdW heterostructure exhibits an indirect band gap of 2.60 eV with a Type-I band alignment. The optical gap of the heterostructure is found to be 2.64 eV, with an exciton binding energy of 0.71 eV, both reduced compared to those in the isolated monolayers. Moreover, we investigate the temperature-dependent optoelectronic behavior of the heterostructure, considering electron-phonon coupling. A zero-point renormalization of 0.04 eV in the direct band gap is observed. While the direct band gap decreases monotonically with temperature from 0 K to 400 K, the indirect band gap displays a non-monotonic trend. As a result, the absorption spectrum undergoes a meaningful redshift with increasing temperature. At room temperature, the optical gap of the heterostructure is reduced to 2.51 eV and the exciton binding energy to 0.63 eV. Our findings highlight the important role of electron-phonon interaction in the optoelectronic response of ZrS2/HfS2 vdW heterostructure, supporting its use in high-performance optoelectronic devices.